Vehicle suspension systems have as their goal the control of chassis motion during vehicle operation. One operating motion characteristic, which is controlled by known suspension systems, is chassis roll. A vehicle experiences chassis roll during a turning maneuver. During chassis roll, the chassis tilts or "rolls" about the vehicle's fore-to-aft axis toward an outside direction of the turn.
It is known to counteract the roll effect of the chassis by providing an opposing force to the chassis. Several methods are known to apply the opposing force. One method includes applying a chassis lifting force via corner actuators located on the vehicle side that is on the outside of the turn and/or a chassis lowering force via corner actuators located on the vehicle side that is on the inside of the turn.
Another known method is to utilize a stabilizer bar that extends laterally across the vehicle. The stabilizer bar, which is also known as a roll-control bar, acts as a torsion spring to apply the opposing force. Further, it is known to vary the opposing force that the stabilizer bar applies to the chassis. One way to vary the opposing force is to utilize and control one or more hydraulic actuators in the connection of the stabilizer bar. An example of such a system is shown in U.S. Pat. No. 5,362,094 to Jensen.
To determine the amount of roll-opposing force to be applied to the chassis, such active suspension systems require an indication of lateral acceleration to which the vehicle is subjected during the turning or cornering maneuver. In one known system, an estimated value of lateral acceleration is calculated. The lateral acceleration calculation requires a sensory input from a steerable road wheel angle sensor, a sensory input from a vehicle velocity sensor, and the value of the vehicle wheel base dimension. In one example, the road wheel angle sensor is a steering shaft angle sensor and the vehicle velocity sensor is a drive-train (e.g., transmission) sensor.
The accuracy of the calculated estimate is dependent upon the accuracy of the relationship of the road wheel angle sensor and the vehicle velocity sensor to the actual lateral acceleration being experienced by the vehicle. The signals from the road wheel angle sensor and the vehicle velocity sensor may not accurately reflect the actual lateral acceleration experienced due to terrain conditions over which the vehicle is being driven. For example, driving the vehicle on a low traction surface may result in some amount of road wheel slippage. The calculated lateral acceleration, in this wheel slippage example, would not equal the actual lateral acceleration experienced by the vehicle.
Other known systems have a physical lateral acceleration sensor mounted to the vehicle and which provides a signal indicative of sensed actual lateral acceleration. However, the signal provided by the lateral acceleration sensor may include high frequency components resulting from road noise. One solution for eradicating such high frequency noise is to digitally low-pass filter the output signal from the acceleration sensor. However, use of a low-pass filter introduces a phase lag into the control system and thereby degrades the system's performance by reducing the system's bandwidth and the system's ability to quickly respond to steering maneuvers.